1. Field of the Invention
The present invention relates to a shop apparatus for an anonymous order, a purchaser apparatus, a purchaser identity proving apparatus, and a purchaser identity verifying apparatus using a group signature scheme.
2. Description of the Related Art
In the field of providing online sales service, techniques using a group signature scheme (for example, D. Chaum, E. Van Heyst, “Group Signatures”, EUROCRYPT '91, LNCS 547, Springer-Verlag, pp. 257-265, 1991, G Ateniese, J. Camenisch, M. Joye and G. Tsudik, “A Practical and Provably Secure Coalition-Resistant Group Signature Scheme”, CRYPT 2000, LNCS 1880, Springer-Verlag, pp. 255-270, 2000. Atsuko Miyaji, Hiroaki Kikuchi, “Information Security”, Ohm, ISBN4-274-13284, pp. 112-114) has been proposed from the viewpoint of realizing protection of personal information and privacy (for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-054905, 2004-320562 and 2006-119771).
In the proposed techniques, protection of personal information and privacy of users is realized by anonymity and unlinkability. Anonymity mentioned here refers to the property that prevents disclosure of personal identity. Unlinkability refers to the property of the inability to judge whether two different authentication requests are made by the same user.
The proposed techniques have traceability, and realize separate payments for each service in a usual operation and specification of an unauthorized user upon occurrence of an illegal access, at the same time. Traceability is a function in which only a predetermined personal information managing organization other than a service provider can identify a user.
However, although unlinkability is an important property from the viewpoint of protection of personal information and privacy, it may cause inconvenience to a service provider. For example, when a user wants to inquire about or return purchased goods and services, as unlinkability is given to the purchased goods and services, such user's requests may not be directly handled only between the user and service provider. Further, when the same user repeatedly uses the same service provider, as unlinkability is given to the purchased goods and services, the number of times the user uses the service provider is unknown. This means that benefits such as offering point services or the gathering of market information regarding usage cannot be carried out.
In the service providing systems used prior to the above-mentioned proposed techniques, as a person is always identified, although actions to inquire/request return of merchandise and provision of point service are easy to provide, protection of personal information and privacy is difficult to realize.
In the above proposed techniques, as unlinkability is always maintained, a high level of protection of personal information and privacy can be realized. On the other hand, having unlinkability may make it difficult to inquire based on past use or request to return merchandise, or provide point service based on past use.